We can now turn to defining \(\delta ^{\prime }\)  from \(\delta \) . To avoid unsightly \((-)^{\mathrm {op}}\)  symbols appearing everywhere we simply consider \(\mathsf {P},\mathsf {P}^{\prime },\mathsf {S},\mathsf {S^{\prime }}\)  to be contravariant functors throughout (as opposed to covariant functors from/to an \((-)^{\mathrm {op}}\)  category). The following definition was given in [1]}.
